Aging is associated with a decline in the ability of the individual to mount protective immune responses. Although it is clear that T cells and antigen-presenting cells have decreased function with age, we have shown that elderly individuals have intrinsic defects in B cells, compromising their responses to vaccines. These defects include the reduction in activation-induced cytidine deaminase (AID), necessary for class switch recombination and somatic hypermutation which are both required for the generation of optimal antibody responses and immunological memory. We have previously identified B cell-specific biomarkers able to either monitor or predict the response of an individual to the influenza vaccine. Specifically, AID in response to CpG, the ex vivo percentage of switch memory B cells and B cell cytoplasmic TNF-a, all measured before vaccination, significantly correlate with the in vivo serum response and therefore we have proposed these as predictive markers of response. In this grant we will test whether B cell function, the specific markers above, and particulat B and T cell subsets are impaired in the elderly, in young individulas which do not respond to vaccination and in those that contract respiratory tract infections. We have recently unexpectedly found that the B memory response to the influenza vaccine may not be reduced in the elderly, at least to a repeated vaccine and the current competing renewal will extend our previous studies on the vaccine response by pursuing mechanisms for decrease in B memory and/or plasmablast and plasma cell function in elderly and younger individuals. Objectives of this R01 competing renewal application are to determine which B cell subsets and B cell-specific biomarkers are responsible for and predictive of the primary and memory in vivo responses to the influenza vaccine in young and elderly and the contribution of particular T cell subsets to this. We will determine further molecular mechanisms responsible for the down- regulation of primary and memory antibody responses in aged individuals, including candidate transcription factors and signaling pathways, contribution of inflammation and the serum microbiome and miRNAs. Lastly, we will continue our novel studies with small molecules to improve the impaired in vitro B cell responses in the elderly. These studies are focused on the influenza vaccine response but should be relevant for other vaccine responses as well as the general state of immune responsiveness in the elderly and the adult controls. The results of these studies should help to prevent infectious diseases and improve the biological quality of life in the elderly.